Acoustic field structure in the first oceanic convergence zone for different frequencies in the audio range

Experimental data on the angular and energy structures of the acoustic field generated in the first convergence zone by a source of continuous pseudo-noise radiation in the frequency range 0.5–4.0 kHz are presented. The experiments are carried out in a tropical region of the Central Atlantic. The acoustic field characteristics are studied with the omnidirectional and highly directional (～2°) reception in the vertical plane. Particular attention is given to studying the field structure at the entrance to the convergence zone at frequencies of 1.25 and 3.15 kHz. The experimental data are compared with the ray calculations. In the experiments, the origin of the convergence zone, which is determined by a sharp increase in the received signal intensity, is found to be about 1.2 km nearer to the source than in the calculations. At a frequency of 1.25 kHz, the convergence zone begins 300 m nearer than at the higher frequency (3.15 kHz). At distances of several kilometers to the zone origin, weak signals that arrive at the same angles as the signals forming the origin of the convergence zone are detected.